In a UMTS (Universal Mobile Telecommunications System) network, attempts are made to optimize features of the system, which are based on W-CDMA (Wideband Code Division Multiple Access), by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), for the purposes of improving spectral efficiency and improving the data rates. With this UMTS network, long-term evolution (LTE) is under study for the purposes of further increasing high-speed data rates, providing low delay, and so on (non-patent literature 1).
In the third-generation system, a transmission rate of maximum approximately 2 Mbps can be achieved on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in the LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band which ranges from 1.4 MHz to 20 MHz. Furthermore, with the UMTS network, successor systems of LTE are also under study for the purpose of achieving further broadbandization and higher speed (for example, LTE-Advanced (“LTE-A”)). The system band of the LTE-A system includes at least one component carrier (cell), where the system band of the LTE system is one unit. Widening the band by gathering a plurality of component carriers like this is referred to as “carrier aggregation.”
In radio communication, as uplink and downlink duplexing methods, there are frequency division duplexing (FDD) to divide the uplink and the downlink by frequency and time division duplexing (TDD) to divide the uplink and the downlink by time. In release-10 LTE, when carrier aggregation is executed in TDD, as shown in FIG. 1A, the ratio between uplink subframes and downlink subframes (transmission time intervals: TTIs) is the same in all component carriers. In release-11 LTE, considering application of a heterogeneous network and so on, as shown in FIG. 1B, changing the ratio between uplink subframes and downlink subframes in each component carrier when carrier aggregation is executed in TDD, is under study.
Meanwhile, when broadbandization is achieved by increasing the number of component carriers (the number of carrier aggregations) to use for communication between a radio base station apparatus and a user terminal, as shown in FIG. 2, for example, it is possible to multiplex and transmit downlink control information (DCI 2) for a downlink shared channel to be transmitted in a component carrier CC 2 (S-cell (Secondary-cell)) over a downlink control channel (PDCCH) of another component carrier CC 1 (P-cell (Primary-cell)) (cross-carrier scheduling). Here, in order to identify in relationship to which component carrier (CC 1 or CC 2) the downlink control information (DCI 2) provides downlink shared channel information, a DCI configuration in which a carrier indicator (CI) is attached is adopted. The field to represent the carrier indicator (CI) is the CIF. That is to say, when DCI for a shared data channel demodulation to be multiplexed on the data field of a given component carrier is multiplexed over the control channel field of another component carrier, a CIF to represent the index of the component carrier (carrier index) where the shared data channel to be demodulated is multiplexed, is added to the DCI.